She lives in Bristol and works in Bath. But Louise Clarke became convinced she was French.

A rare brain disorder left the 30-year-old recruitment consultant believing she was living in Paris.

She started speaking French all the time, rang her friends to invite them to stay in the French capital - and asked to eat croissants.

She was also plagued by migraines and hallucinations and ended up so confused that her worried family took her to hospital.

After months of tests, she became one of only 200 people in the world to be diagnosed with Susac's Syndrome.

The disorder is thought to be brought on by stress and affects the brain, ears and eyes, mainly among young women. In Miss Clarke's case, it appears to have brought back memories from when she was living in France four years ago and confused them with the present.

"It might sound funny to others, but suddenly thinking you are French is terrifying," she said.

In October 2004, she began to become confused, disorientated and suffered cloudy vision. "It started with migraines and hallucinations," she said. "I eventually got so confused that my sister took me to A&E.

"I was gabbling away in French in my hospital bed. It was a really tough time for my family.

"At one point, my sister discovered I had phoned all my friends and told them to come and visit me in Paris. She had to ring them all back to explain what had happened." Miss Clarke also thought she was in Vietnam, a country she had visited a few months before she became ill.

She spent three months at the Royal United Hospital in Bath while doctors carried out test after test. She was eventually diagnosed with Susac's syndrome. It is thought to be an autoimmune condition, which means the symptoms result from the immune system attacking healthy tissue.

Typically, it causes alterations in the brain, leading to memory problems, behaviour changes and an inability to concentrate.

As Miss Clarke's case shows, it can also make the sufferer think they are living in a memory of something they experienced months or years earlier.

Miss Clarke, who still has the syndrome, is able to control it with steroids and other medication but has been told it can last up to five years.

Professor Michael Hahn, an American expert who has investigated the syndrome, said Miss Clarke was not alone in suffering such bizarre symptoms.

"I've studied around 40 cases and a fair percentage reported the confusion of believing they were in a foreign country or place they had visited," he said.

•Susac's Syndrome is named after Dr John Susac, who first spotted the problem in 1975. Sufferers often experience a personality change and develop bizarre and paranoid behaviour. Their speech can be affected, and many experience unrelenting and intense headaches and migraines, some form of hearing loss, and impaired vision. The problem usually corrects itself, but this can take up to five years.